A larger-than-life character, this former Fleet Air Arm pilot drove a Maserati before managing to get hold of a Lago-Talbot which he raced during the 1951 season, taking second place in the International Trophy and fifth in the non-championship Dutch GP. With Formula 2 becoming the premier category for 1952, his car was redundant except for Libre events, so Duncan thereafter had a handful of outings in John Heath's HWMs. His best placings were fourth in the 1952 Eifelrennen, and sixth in the Ulster Trophy at Dundrod and the Crystal Palace Trophy in '53.

However, his greatest moments came in sports car racing. Having finished sixth at Le Mans with a Nash-Healey in 1951, Hamilton won the race two years later in a works Jaguar D-Type shared with Tony Rolt. The pair returned the following season, this time in Duncan's own D-Type, and finished second after a thrilling chase of Gonz?lez's Ferrari in the wet. Hamilton scored further major wins in the Coupe de Paris at Montlh?ry in '54 and '56 and the 1956 Reims 12 Hours with Ivor Bueb. There were numerous excellent placings elsewhere, including a third in the 1956 Swedish GP when Duncan shared a works Ferrari with de Portago and Mike Hawthorn. It was after the death of his close friend early in 1959 that Duncan retired from racing to concentrate on his successful garage business.